Vehicle-acceleration-sensitive (or “vehicle sensitive”) sensor devices serve in general to block the belt extraction of a seat belt from a belt shaft of the belt retractor in the event that a predetermined deceleration- or acceleration-threshold value acting on the vehicle is exceeded and to restrain the occupants for their own safety. For this purpose, the sensor devices include, among other things, a ball- or mushroom-shaped inertial mass, which is supported on a contact surface or abutment surface. The response behavior of the sensor device is determined by the mass of the inertial mass, by the shape of the inertial mass, and by the shape of the contact surface or of the abutment surface in the sensor device. For the case that the deceleration- or acceleration-threshold prescribed by the design of the sensor device is exceeded, the inertial mass is deflected so far out of its rest position in an inertia-dependent manner that it deflects a blocking lever, which in turn controls a blocking device of the belt retractor for blocking the belt shaft by engaging in a gearing of a control disc. The blocking device will not be described here in more detail since it is sufficiently well known in the prior art and is not part of this invention.
Such sensor devices are in principle problematic if they must be provided in belt retractors that are to be arranged to be mounted to a tilt-adjustable backrest. In such a case the sensor devices must also be functional in different orientations or angular positions of the belt retractor.
A belt retractor is known from EP 1 893 455 B1, for example, wherein the sensor device includes a pivotable sensor housing wherein the inertial mass is supported. The sensor housing is supported such that in the event of an adjustment of the backrest or of a folding down of the backrest, it can orient itself automatically. However, so that the belt shaft is subsequently blocked according to the legal requirements, in the event of an exceeding of the predetermined threshold values of vehicle deceleration, the sensor housing is blocked during the extraction movement of the seat belt. The blocking of the sensor housing is affected by a blocking device including a pivotable blocking lever, which releases the sensor housing to orient the sensor housing in the event of a rotating of the belt shaft in the belt retraction direction, and blocks during the belt extraction movement by engaging in a gearing of the sensor housing.
A problem of such a self-orienting sensor device is that due to the pivotability of the sensor housing in the direction of the pivot direction, the sensor device can have a response behavior other than transverse to the pivotability of the sensor housing. This is because with accelerations acting in the direction of pivotability, the sensor housing can pivot along slightly, until it is blocked, so that consequently only with a large vehicle deceleration is the inertial mass displaced far enough to control the blocking device of the belt retractor. The response curve of the sensor device is thus higher in the direction of pivotability than transverse to the direction of pivotability.
The object of the invention is therefore to provide a belt retractor including a self-orienting vehicle-acceleration-sensitive sensor device wherein the difference, caused by the pivotability of the sensor housing, of the response curves of the sensor device in the direction of pivotability and transverse to the pivotability of the housing is reduced.